Rabio transformer



y 1931. T. D. YENSEN 1,807,022

RADIO TRANSFORMER Original Filed March 29, 1924 INVENTOR Tryj've D.)ensen Y Frequeflcy Scale) W'd L 60 I00 300 500 min 000 40 00 ATTORNEY Patented May 26, 1931 UNITED STATES PATENT OFFICE TRYGVE D. YENSEN, OF FOREST HILLS, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 8:; MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA RADIO TRANSFORMER 15, 1930. Serial N0. 428,660.

My invention relates to transformers and more particularly to radio or audio-frequency transformers having a core composed of an iron-nickel alloy. and is a continuation, in part, of my application N 0. (565,406, nled on September 28, 1923, and a division of my application N 0. 702,897, filed. on March 29, 1924.

The principal object of my invention is to provide a radio or audio-frequency transformer having a core composed of an ironnickel alloy that has certain magnetic characteristics which render it especially suitable for building up the signal current in radio receiving systems employing one or more receiving and amplifying tubes.

Another object of my invention is to provide a radio or audio-frequency transformer having a core composed of an iron-nickel alloy that has-a high specific resistance, a low hysteresis loss, and comparatively high permeability at low magnetizing forces.

In radio receiving systems employing one or more receiving and amplifying tubes, a transformer is generally inserted in each tube circuit for the purpose of increasing the strength of the signals for further detection or amplification by the next tube circuit.

The signal received by the first tube is very weak, and it is, therefore, essential that the core material shall have a high specific resistance to avoid undue loss by eddy currents. Since the tlOtit-PMIIOllIlt of current impressed upon the transformer is small, it is also desir-able that the core material shall have high permeability at low magnetizing forces.

It has previously been the practice to employ either iron or an iron-silicon alloy as a proximately four and one-half times that of pure iron and it has a considerably higher permeability than either commercial iron or iron-silicon alloys,at loW magnetizing forces. For example, within the range of H-Ol to H=.1, my improved alloy has a maximum permeability between 20,000 and 100,000.

My invention will be better understood by reference to the accompanying drawings, in which Figure 1 is a graph showing the relation between the induction of my "'"proved ironnickel alloy and that of an iron-silicon alloy containing 4 of silicon, at low magnetizing forces,

Fig. 2 is a circuit containing a three-electrode tube, a source of primary current and my improved transformer, and

Fig. 3 is a graph showing the amplification ratio, atdifferent frequencies, of myimproved iron-nickel alloy, as compared with Original-application filed March 29, 1924, Serial No. 702,897. Divided and this application filed February numeral 1 designates the magnetization curve of an iron-silicon alloy containing approximately 4% of silicon and the numeral 2 desig nates the magnetization curve of my improved iron-nickel alloy. It will be noted that the magnetization curve of the ironnickel alloy is much steeper than the magnetization curve of the iron-silicon alloy.

Referring to Fig. 20f the drawings, the numeral 3 designates avacuum tube, of the three-electrode type, which is connected in series with an audio-frequency transformer 4 by means of a conductor 5 having a series of primary turns 6. Direct current is supplied to the tube plate by means of the usual B-battery, and a conductor 7, having a secondary winding with a considerably larger number of turns than the primary Winding, is connected to the transformer for the purpose of transmitting the incoming signals, at a higher voltage, to an additional tube for further amplification or detection.

As will be readily understood, when the core of the transformer is subjected to the in-' fiuence of the primary circuit, flux is induced therein Which varies in accordance with the strength of the plate or primary current. The amount of flux induced in the core, however, does not increase in direct proportion to the increase in current but in accordance with the magnetization curve. For instance, as shown in 1 of the drawings, when an iron-silicon alloy 1S utilized in the core, the

flux increases in accordance with the line a transformer composed of my improved iron-nickel alloy by a magnetizing force represented by thelin'e ON.

lVhen an alternating-current signal is applied between the grid and the filament of the tube having a definite frequency and amplitude, the magnetizing force will pulsate between the limits ON and OP, the amplitude of the pulsations depending upon the strength of the signal and their number depending upon the frequency of the signals. These pulsations will produce changes in the magnetizing forces varying from ON to OP. When the magnetizing force increases from Mto N, the induction increases from a to I), in the case of the iron-silicon alloy, and from 0 to d, in the case of my improved iron-nickel alloy. When the magnetizing force decreases from N to P, however, the induction no longer follows the magnetization curve but decreases only to the point E where an iron-silicon alloy is employed and to the point F when an iron-nickel alloy is employed. As the magnetizing force pulsates between P and N, the flux pulsates correspondingly, following the displaced hysteresis loops G- and I, as indicated by the arrows. The maximum flux induced in the iron-silicon alloy by the signal current will be AB and the maximum flux induced in the iron-nickel alloy will be A13 It will be noted that the amount of flux induced in the iron-nickel alloy will be considerably greater than that induced in the iron-silicon alloy for the same change in magnetizing force.

In radio circuits of certain types, such as,

and A13 In such circuits, it will be noted that the change'in induction for the iron silicon alloy is very much less than for my improved iron-nickel alloy.

In Fig. 3 of the drawings, the solid curves 8 and 9 show the comparative performance data for an audio-frequency transformer having cores composed, respectively, of an ironsilicon and an iron-nickel alloy, the transformers being identical, with the exception of the core material. The ordinates cesignate the total amplification ratio between the applied grid voltage and the secondary transformer voltage. The abscissa designates the signal frequency, plotted to a logarithmic scale so that the effect ofthe low-frequency part of the scale may be shown more clearly. The dotted'lines 10 and 11 represent the respective ratios which may be obtained from cores composed of iron-silicon and iron-nickel alloys when the direct-current components of the primary circuit is eliminated, either by the push-pull circuit or by other means. The gain in amplification ratio, -by the utilization of my improved iron-nickel alloy is of special importance in the .case 'of lowfrequency music, such as that produced by the organ. For a single stage of amplification, the ratio is two to one. When two or more stages of amplification are employed,

the reproduction quality is very much better when an iron-nickel core is utilized. For instance,. if the gain at sixty cycles is three to one for a single stage of. amplification, it Will he twenty-seven to one for three stages of amplification, thus ensuring a greatly im,

proved quality of reproduction, especially for v certain types of music.

In practicing my invention, I. provide an alloy of nickel and iron in approximately equal proportions, for example, 40% to 60% nickel and 60 to 40% iron,'preferably utiliz-.

ing an alloy containing 50% of each ingredient. I prefer to utilize relatively commercially pure metals although a small amount of minor impurities will necessarilybe present.

The alloy may be prepared in any suitable manner, as by melting together the desired proportions of iron and nickel in a suitable crucible, heated in any suitable manner. I prefer to melt the material in a reducing or nonoxidizing atmosphere, in an electric furnace. A small amount of metal capable of rendering the alloy more readily forgeable,

such as manganese, may be added. The alloy is then castand rolled to the desired thickness.

The rolled material is next annealed by a process which consists in placing it in a sealed furnace, preferably under slight pressure, passing a stream of hydrogen through the furnace and heating it to a high temperature, for instance, at 1200 C. for from 2 to 8 hours.

The material is then cooled in the furnace to 500 O. at any convenient rate. Cooling the material in the furnace at the rate of approximately to 100 0. per hour down to. a

temperature of about 500 C. gives good re sults. The furnace may then be opened, precaution having first been taken to remove the hydrogen therefrom by any suitable means, as by displacement by nitrogen, to prevent explosion. The material is then allowed to cool, either in the furnace or in air, to room temperature without attempting to control the rate of cooling.

By this treatment, the maximum permeability of 14 mill sheets has been increased up to from 20,000 to 100,000, and the hysteresis loss reduced to as low as 150 to 600 ergs per cubic centimeter per cycle for B=10,000 gausses. When commercially pure materials, such as armco iron and electrolytic nickel are employed, and all moisture is eliminated from the annealing furnace, a maximum permeability ranging from 30,000 to 60,000 is usually obtained. i

The exact reason why the hydrogen treatment increases-the permeability of the material, especially at low magnetizing forces, is not definitely known. It is believed, however, that the remarkable improvement in permeability results fromthe elimination or partial removal of certain impurities, such as. oxygen, nitrogen, sulphur and carbon.

Similar results may be obtained by varying .the factors in the annealing operation, such as time and temperature. For example, I may employ temperatures ranging from 900 to 1400 C. Higher temperatures shorten the annealing operation but increase the cost of'the furnace operation, while, at lower temperatures, a relatively longer time is necessary to secure the results obtainable in a: few hours at 1200 C.

After the annealing operation, the material is punched into ring or L-shape forms and again subjected to a short annealing operation to relieve the punching strains. The punchings are preferably coated with an insulating material, such as a suitable varnish or sodium silicate. If sodium silicate is employed, it is applied in the form of an aqueous solution and subsequently dried and baked. The punchings are then assembled in the usual manner.

An alternate method consists in first preparing the punchings from the rolled material and subjecting them to the hydrogen annealing operation. This method renders the second annealing operation unnecessary;

The high permeability of my improved material at low magnetizing forces and its low hysteresis loss, as compared with that of silicon steel, which is the best previously knownmaterial utilized for the vcore of radio transformers,- indicates clearly the superiority of my improved alloy for use'in audio-frequency transformers. Furthermore, the high resistance of iron-nickel alloys, when the ingredients are present in apbelow 600 ergs proximately equal proportions, reduces the eddy current losses to a low value and, consequently, the total power loss in the transformer will be low.

While I have described my invention in considerable detail, it will be understood that specific examples should be construed as 11- lustrative and not by way of limitation, and,

'in View of the numerous modifications which may be effected therein Without departing from the spirit and scope of my invention, it is desired that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention 1. A radio transformer having a core com- .prising an alloy of iron and nickel in apequal proportions, said alloy having a hysteresis loss of 150 to 600 ergs per cubic centimeter per cycle for B=10,000 gausses.

3. A radio transformer core, comprising laminations composed 'of a heat-treated al having a -maximum permeability ranging from 20,000 to 100,000 and a hysteresis loss less'than600 ergs per cubic centimeter per cycle for B=l0,000 gausses.

4. An audio-frequency transformer core I having laminations containing from 40% to nickel and iron and minor impurlties as the remaining percentage, said laminatlons having a maxlmum permeability ranging from 20,000 to 100,000..

5. An audio-frequency transformer comprising a primary winding, a secondary winding and a core comprising laminations containing 40% to 60% nickel and iron and minorimpuritie's as the remaining percentage, said laminations having a hysteresis loss per cubic centimeter per cycle for B=10,000.

6. An audio-frequency transformer core having laminations composed of an alloy containing iron as one of the principal ingredients and from 40% to 60% nickel, said alloy having a maximum permeability ranging from 20,000 to 100,000.'

7 A radio transformer having a core containing laminations comprising 40% to 60% iron and nickel and minor impurities as the remaining percentage, said laminations having a maximum permeability ranging from 30,000 'to 60,000.

8. An audio-frequency transformer having a primary winding, a secondary winding and core laminations comprising 40% to 60% nickel and a remainder of iron and minorimpurities', said laminations having a p: r-

loy composed of iron and nickel in approximately equal proportions, said laminations meability between 30,000 and 60,000 at magnetiz ing forces ranging from H=.1 to H=1,

and a hysteresis'loss between 15Qand 600 ergs per cubic centimeter per cycle for B=10,000 gausses. I

' In scrib testimony whereof, I have hereunto subed my name this 6th day of February,

TRYGVE D. YENSE'N. 

